This invention relates to a process for recovery of crude oil from a geological formation containing it. In a particular aspect, this invention relates to recovery of crude oil by the micellar-flood process.
The yield of crude oil from a geological formation is usually far from the total crude oil present because once the pressure on the formation is relieved, there is no easy method for recovering the residual oil.
It is known to improve recovery of residual crude oil from a geological formation containing it by the process of water-flooding. In this process, one or more wells spaced from the production well are drilled and water under pressure is pumped through these auxiliary wells into the surrounding formation. The advancing water front sweeps residual oil before it to the production well where both water and oil are recovered. However, considerable petroleum is left behind in the formation and there have been numerous attempts to improve its recovery.
A variety of processes have been proposed to improve this recovery. One of these, as proposed by Gogarty et al, U.S. Pat. No. 3,254,714, which is incorporated herein by reference thereto employs injection of micellar solutions (also known as micro-emulsions, swollen micells and soluble oils). Basically these solutions are water-in-oil type emulsions composed of a surfactant, a hydrocarbon and water and may also contain small amounts of electrolytes and cosurfactants. Oil-in-water emulsions have also been used. These solutions are stable in the presence of reservoir water and rock and can be driven through the reservoir with water. They displace most if not all of the oil contacted, but due to channeling, some portions of the formation may be by-passed. The process can be used in either secondary or tertiary recovery operations.
According to Gogarty et al, "Miscible-Type Water-flooding: Oil Recovery with Micellar Solutions", J. Pet. Tech., 1407-1414, December 1968, the process is operated as follows. A slug of a micellar solution is injected to serve as the oil-displacing agent. Then a mobility buffer is injected to protect the slug from water invasion and finally drive water is injected to push the slug and mobility buffer through the reservoir. The mobility buffer is either a water-external emulsion or water thickened with a polymer. As the slug moves through the reservoir, the residual crude oil is displaced from the reservoir and dissolves in the hydrocarbon phase of the micellar solution. The mixture is recovered at the producing well.
As previously mentioned, micellar solutions consist primarily of three components, i.e. hydrocarbon, surfactant and water, and optionally electrolytes and co-surfactants. The hydrocarbon can range from liquified petroleum gas through various refinery streams to crude oil. Sodium salts of petroleum sulfonic acids are effective and widely used surfactants but other types are also used.
Lower alkyl alcohols are often added as co-surfactants. They increase the latitude in composition through which micellar solutions can be made. Electrolytes allow additional control in attaining the proper viscosity required for mobility control, i.e. control of the movement of the slug through the reservoir.
Gogarty et al, J. Pet. Tech., op. cit., list the compositions of six typical micellar solutions, which can be summarized as follows:
______________________________________ Petroleum sulfonate 8.6-14.3% by volume Isopropyl alcohol 0.6-4.3 Water 11.7-40.0 Hydrocarbon 45.6-73.4 Sodium sulfate 0-0.2* ______________________________________ *Wt % based on water.